As a communication system for connecting a host computer with a device (such as a printer, a scanner, a digital camera, or the like), wireless USB is known. A single device can be shared between a plurality of host computers through wireless USB.
With wireless USB communication, however, the single device is unable to simultaneously communicate with the host computers. Therefore, it performs one-to-one communication with each of the host computers, as stipulated in wireless USB standard (Wireless USB Specification Rev. 1.0).
In the following, a process for establishing communication connection between a host computer and a device is described with reference to FIG. 12 for an exemplar case where a digital multi-function peripheral is used as the device. It should be noted that the digital multi-function peripheral (MFP) is an apparatus having plural functions (such as copying function, printing function, scanning function, facsimile function, and memory card read/write function) andused to accomplish efficient office work.
FIG. 12 is a view for explaining a process for establishing communication connection through wireless USB. In the illustrated system, wireless USB communication is performed between a host PC 1000 having a wireless USB antenna 1001 and a device 2000 having a wireless USB antenna 2001.
The host PC 1000 has a function of transmitting a beacon via the wireless USB antenna 1001. As shown in FIG. 13, a host
ID 1002 unique to the host PC 1000 and a device ID 2002 unique to the device 2000 are indicated in the beacon.
To request the device 2000 to execute a print job created by an application running on the host PC 1000, the host PC 1000 transmits a beacon to the device 2000. The device 2000 that receives the beacon reads a device ID 2002 indicated in the beacon, and confirms whether the device ID 2002 is the same as its own device ID. If the device ID 2002 differs from the own device ID, the device 2000 determines that the beacon is not directed to the device 2000 and discards the beacon.
Next, the device 2000 reads the host ID 1002 indicated in the beacon, and confirms in terms of association whether the host ID 1002 is equal to one of host IDs registered in the device 2000. If no such host ID is registered, the device discards the beacon, determining that no association has been set for the host PC. It should be noted that association is an initial connection process performed at the time of installation of wireless USB equipment in order that a CC (Connection Context) comprised of a host ID, a device ID, and a connection key is shared between a host PC and a device, and has three phases: identification, authentication, and authorization.
Next, the device 2000 transmits a connection request to the host PC 1000. When authorizing the connection request, the host PC 1000 transmits spooled print data to the device 2000. After completion of print data transmission, the host PC disconnects communication so as not to appropriate the device 2000. At that time, a disconnection request can be transmitted either from the host PC or from the device. As described above, one-to-one wireless USB communication connection is established.
On the other hand, in a case where a single device is shared between a plurality of host PCs, communication connection is established by listing host information in the order in which the device receives beacons from the host PCs and by sequentially transmitting connection requests to the host PCs based on the list. Thus, communication connection between the device and a sequentially selected one of the host PCs is established.
With reference to FIGS. 14 to 16, a description is given of a concrete system where a single device is shared between two host PCs. In FIG. 14, there is shown a case where first and second print jobs are respectively transmitted from first and second host PCs 1000, 1100 to the device 2000. A process sequence is shown in FIG. 15, and an example of host list is shown in FIG. 16.
The first host PC 1000 transmits to the device 2000 a first beacon 1000a as a print job processing request (step S6000). The device receiving the beacon requests the first host PC to establish wireless communication connection (step S6001). The first host PC establishes wireless communication connection with the device and then transmits print data for the first print job to the device (step S6002). After completion of processing on the print data by the device, the first host PC or the device requests disconnection of the wireless communication connection (step S6003).
The second host PC 1100 transmits to the device 2000 a second beacon 1100a as a print job processing request (step S6100). At that time, the device is in a state where wireless communication connection with the first host PC 1000 is established. Thus, after completion of processing on the first print job, the device disconnects wireless communication connection with the first host PC, and requests the second host PC to establish wireless communication connection (step S6101). The second host PC establishes wireless communication connection with the device, and then transmits print data for the second print job to the device (step S6102). After completion of processing on print data by the device, the second host PC or the device disconnects the wireless communication connection (step S6103).
The order in which the host PCs are connected is controlled based on a host list 1200 shown in FIG. 16. The host list 1200 is stored in a memory of the device 2000, and is comprised of a number field 1201 and a host name field 1202. The device registers into the host list 1200 host information in the order in which beacons from host PCs are received. In the number field 1201, there are shown the order in which connection requests are delivered as well as the order in which beacons are received.
It should be noted that the wireless USB communication system as described above is disclosed in, e.g., PTL (Patent Literature) 1 listed below.
Conventionally, file systemmount control (by which a memory is made accessible from a computer) has been known, in which a host PC establishes wireless communication connection with a device, and mounts as a file system a memory card attached to the device. In a digital camera and a digital multi-function peripheral, a construction has been realized where a host PC accesses a file stored in a memory card and reads the file from the memory card. A digital multi-function peripheral of this type has a memory card reader writer for reading and writing data from and into a memory card.
For example, in an information processing apparatus disclosed in PTL (Patent Literature) 2 listed below, data recording means is unmounted (or controlled to a state unaccessible from a computer) when it is determined that there is an apparatus connected to a device, but mounted again when it is determined that the connection between the device and the apparatus is disconnected. Thus, file system mount control can be made according to whether or not any apparatus is connected to the device.
With the above-described conventional arrangement where a digital multi-function peripheral (device) having a memory card reader writer is shared between a plurality of host PCs, the device is able to recognize completion of a print job requested from the device to the host PC, but a problem is posed that a memory card job by a host PC that mounts a memory of the device cannot be completed until the host PC unmounts a file system.
Unlike a print job, completion of a memory card job is controlled by the host PC having requested the memory card job. Thus, even when receiving a job request from another host PC, the device cannot immediately start communication with the other host PC. If the device forcibly disconnects communication with the host PC when the memory card job is being executed, the file system is forcibly dismounted from the host PC, and an error state of the host PC is caused, resulting in a fear that a file is destroyed in some cases.
If the memory card is left mounted even after a host PC user completes an operation for accessing the memory card of the device, a problem is posed that the device is appropriated solely by the one host PC.